Insect pests are a major factor in the loss of the world's agricultural crops. Insect pest-related crop loss from corn rootworm alone has reached one billion dollars a year. For example, corn rootworm feeding can be economically devastating to agricultural producers. The western corn rootworm is a major insect pest of corn or maize in many regions of the world. While not as important a pest as the western corn rootworm, the southern corn rootworm may occasionally cause significant economic damage to corn. Damage from western and southern corn rootworms may result in increased lodging, reduced drought tolerance and ultimately, crop yield reductions.
Traditionally, the primary methods for impacting corn rootworm populations are crop rotation and the application of broad-spectrum chemical insecticides. Unfortunately, some species of pests have developed resistance to the chemical insecticides. Furthermore, consumers and government regulators alike are becoming increasingly concerned with the environmental hazards associated with the production and use of synthetic chemical pesticides. Because of such concerns, regulators have banned or limited the use of some of the more hazardous pesticides. Thus, there is substantial interest in developing alternative pesticides.
Biological control of insect pests of agricultural significance using a microbial agent, such as fungi, bacteria, or another species of insect affords an environmentally friendly and commercially attractive alternative. Generally speaking, the use of biopesticides presents a lower risk of pollution and environmental hazards, and they provide greater target specificity than is characteristic of traditional broad-spectrum chemical insecticides. In addition, biopesticides often cost less to produce and thus improve economic yield for a wide variety of crops.
Certain species of microorganisms of the genus Bacillus are known to possess pesticidal activity against a broad range of insect pests including Lepidoptera, Diptera, Coleoptera, Hemiptera, and others. Bacillus thuringiensis and Bacillus papilliae are among the most successful biocontrol agents discovered to date. Insect pathogenicity has also been attributed to strains of: B. larvae, B. lentimorbus, B. papilliae, B. sphaericus, B. thuringiensis (Harwook, ed., ((1989) Bacillus, Plenum Press), 306) and B. cereus (WO 96/10083). Pesticidal activity appears to be concentrated in parasporal crystalline protein inclusions, and several genes encoding these pesticidal proteins have been isolated and characterized (see, for example U.S. Pat. No. 5,366,892).
Microbial insecticides, particularly those obtained from Bacillus strains, have played an important role in agriculture as alternatives to chemical pest control. Recently, agricultural scientists have developed cr op plants with enhanced insect resistance by genetically engineering crop plants to produce pesticidal proteins from Bacillus. For example, corn and cotton plants genetically engineered to produce pesticidal proteins isolated from strains of B. thuringiensis, known as δ-endotoxins or Cry toxins, are now widely used in American agriculture and have provided the farmer with an environmentally friendly alternative to traditional insect-control methods. In addition, potatoes genetically engineered to contain pesticidal Cry toxins have been sold to the American farmer. However, while they have proven to be very successful commercially, these genetically engineered, insect-resistant crop plants provide resistance to only a narrow range of the economically important insect pests. Some insects, such as Western corn rootworm, have proven to be recalcitrant, and the level of Bt-toxin resistance is increasing in formerly susceptible populations of some important insect pests.
Although numerous investigators have attempted to make mutant endotoxin proteins with improved insecticidal activity, few have succeeded. In fact, the majority of genetically engineered B. thuringiensis toxins that have been reported in the literature report endotoxin activity that is no better than that of the wild-type protein, and in many cases, the activity is decreased or destroyed altogether. Thus, new microbial insecticides having altered specificity and/or improved pesticidal activity are desired for use in pest-management strategies.